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.TH PTHREAD_RWLOCK_UNLOCK 3C "Mar 23, 2005"
.SH NAME
pthread_rwlock_unlock \- unlock read-write lock object
.SH SYNOPSIS
.LP
.nf
cc -mt [ \fIflag\fR... ] \fIfile\fR... -lpthread [ \fIlibrary\fR... ]
#include <pthread.h>

\fBint\fR \fBpthread_rwlock_unlock\fR(\fBpthread_rwlock_t\fR \fI*rwlock\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBpthread_rwlock_unlock()\fR function is called to release a lock held on
the read-write lock object referenced by \fIrwlock\fR. Results are undefined if
the read-write lock \fIrwlock\fR is not held by the calling thread.
.sp
.LP
If this function is called to release a read lock from the read-write lock
object and there are other read locks currently held on this read-write lock
object, the read-write lock object remains in the read locked state. If this
function releases the calling thread's last read lock on this read-write lock
object, then the calling thread is no longer one of the owners of the object.
If this function releases the last read lock for this read-write lock object,
the read-write lock object will be put in the unlocked state with no owners.
.sp
.LP
If this function is called to release a write lock for this read-write lock
object, the read-write lock object will be put in the unlocked state with no
owners.
.sp
.LP
If the call to the \fBpthread_rwlock_unlock()\fR function results in the
read-write lock object becoming unlocked and there are multiple threads waiting
to acquire the read-write lock object for writing, the scheduling policy is
used to determine which thread acquires the read-write lock object for writing.
If there are multiple threads waiting to acquire the read-write lock object for
reading, the scheduling policy is used to determine the order in which the
waiting threads acquire the read-write lock object for reading.  If there are
multiple threads blocked on \fIrwlock\fR for both read locks and write locks,
it is unspecified whether the readers acquire the lock first or whether a
writer acquires the lock first.
.sp
.LP
Results are undefined if any of these functions are called with an
uninitialized read-write lock.
.SH RETURN VALUES
.sp
.LP
If successful, the \fBpthread_rwlock_unlock()\fR function returns \fB0\fR.
Otherwise, an error number is returned to indicate the error.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR pthread_rwlock_init (3C),
.BR pthread_rwlock_rdlock (3C),
.BR pthread_rwlock_wrlock (3C),
.BR pthread_rwlockattr_init (3C),
.BR attributes (7),
.BR standards (7)
